Base-promoted cyclization of 3-alkynylquinoxaline-2-carbonitriles with CH-acids: A new method for the phenazine ring synthesis

Article abstract of DOI:10.1016/j.tet.2014.05.023

3-Alkynylquinoxaline-2-carbonitriles were directly transformed into 2,3-disubstituted phenazin-1-amines by treating with a CH-acid (diethylmalonate, ethyl cyanoacetate, malononitrile, 2-tosylacetonitrile, 2-(1-methyl-1H-benzo[d] imidazol-2-yl)acetonitrile, nitromethane) and t-BuOK in THF or DMSO. A new cascade process includes nucleophilic addition of a CH-acid carbanion to the CC bond of 3-alkynylquinoxaline-2-carbonitrile, 6-exo-dig cyclization of the intermediate allyl carbanion with the formation of 2,2-disubstituted 1-imino-1,2-dihydrophenazine and its aromatization via elimination of the C(2)-substituent. Several secondary reactions were also disclosed and discussed.